7-1-7. Categorical Ceiling and Visibility Conditions

1. Categorical terms, describing either reported or forecast general ceiling and visibility conditions, are defined as follows:
   1. LIFR (Low IFR). Ceiling less than 500 feet and/or visibility less than 1 mile.
   2. IFR. Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.
   3. MVFR (Marginal VFR). Ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.
   4. VFR. Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.
2. The cause of LIFR, IFR, or MVFR is indicated by either ceiling or visibility restrictions or both. The contraction “CIG” and/or weather and obstruction to vision symbols are used. If winds or gusts of 25 knots or greater are forecast for the outlook period, the word “WIND” is also included for all categories including VFR.

7-1-8. Inflight Weather Advisory Broadcasts

1. ARTCCs broadcast a Convective SIGMET, SIGMET, AIRMET (except in the contiguous U.S.), Urgent Pilot Report, or CWA alert once on all frequencies, except emergency frequencies, when any part of the area described is within 150 miles of the airspace under their jurisdiction. These broadcasts advise pilots of the availability of hazardous weather advisories and to contact the nearest flight service facility for additional details.

   EXAMPLE-
   1. Attention all aircraft, SIGMET Delta Three, from Myton to Tuba City to Milford, severe turbulence and severe clear icing below one zero thousand feet. Expected to continue beyond zero three zero zero zulu.

   2. Attention all aircraft, convective SIGMET Two Seven Eastern. From the vicinity of Elmira to Phillipsburg. Scattered embedded thunderstorms moving east at one zero knots. A few intense level five cells, maximum tops four five zero.
   3. Attention all aircraft, Kansas City Center weather advisory one zero three. Numerous reports of moderate to severe icing from eight to niner thousand feet in a three zero mile radius of St. Louis. Light or negative icing reported from four thousand to one two thousand feet remainder of Kansas City Center area.

7-1-9. Flight Information Services (FIS)

FIS is a method of disseminating meteorological (MET) and aeronautical information (AI) to displays in the cockpit in order to enhance pilot situational awareness, provide decision support tools, and improve safety. FIS augments traditional pilot voice communication with Flight Service Stations (FSSs), ATC facilities, or Airline Operations Control Centers (AOCCs). FIS is not intended to replace traditional pilot and controller/flight service specialist/aircraft dispatcher preflight briefings or inflight voice communications. FIS, however, can provide textual and graphical information that can help abbreviate and improve the usefulness of such communications. FIS enhances pilot situational awareness and improves safety.

1. Data link Service Providers (DSPs). DSPs deploy and maintain airborne, ground-based, and, in some cases, space-based infrastructure that supports the transmission of AI/MET information over one or more physical links. A DSP may provide a free of charge or a for-fee service that permits end users to uplink and downlink AI/MET and other information. The following are examples of DSPs:
   1. FAA FIS-B. A ground-based broadcast service provided through the ADS-B Universal Access Transceiver (UAT) network. The service provides users with a 978 MHz data link capability when operating within range and line-of-sight of a transmitting ground station. FIS-B enables users of properly equipped aircraft to receive and display a suite of broadcast weather and aeronautical information products.
   2. Non-FAA FIS Systems. Several commercial vendors provide customers with FIS data over both the aeronautical spectrum and on other frequencies using a variety of data link protocols. Services available from these providers vary greatly and may include tier based subscriptions. Advancements in bandwidth technology permits preflight as well as inflight access to the same MET and AI information available on the ground. Pilots and operators using non-FAA FIS for MET and AI information should be knowledgeable regarding the weather services being provided as some commercial vendors may be repackaging NWS sourced weather, while other commercial vendors may alter the weather information to produce vendor-tailored or vendor-specific weather reports and forecasts.
2. Three Data Link Modes. There are three data link modes that may be used for transmitting AI and MET information to aircraft. The intended use of the AI and/or MET information will determine the most appropriate data link service.
   1. Broadcast Mode: A one-way interaction in which AI and/or MET updates or changes applicable to a designated geographic area are continuously transmitted (or transmitted at repeated periodic intervals) to all aircraft capable of receiving the broadcast within the service volume defined by the system network architecture.
   2. Contract/Demand Mode: A two-way interaction in which AI and/or MET information is transmitted to an aircraft in response to a specific request.
   3. Contract/Update Mode: A two-way interaction that is an extension of the Demand Mode. Initial AI and/or MET report(s) are sent to an aircraft and subsequent updates or changes to the AI and/or MET information that meet the contract criteria are automatically or manually sent to an aircraft.
3. To ensure airman compliance with Federal Aviation Regulations, manufacturer's operating manuals should remind airmen to contact ATC controllers, FSS specialists, operator dispatchers, or airline operations control centers for general and mission critical aviation weather information and/or NAS status conditions (such as NOTAMs, Special Use Airspace status, and other government flight information). If FIS products are systemically modified (for example, are displayed as abbreviated plain text and/or graphical depictions), the modification process and limitations of the resultant product should be clearly described in the vendor's user guidance.
4. Operational Use of FIS. Regardless of the type of FIS system being used, several factors must be considered when using FIS:
   1. Before using FIS for inflight operations, pilots and other flight crewmembers should become familiar with the operation of the FIS system to be used, the airborne equipment to be used, including its system architecture, airborne system components, coverage service volume and other limitations of the particular system, modes of operation and indications of various system failures. Users should also be familiar with the specific content and format of the services available from the FIS provider(s). Sources of information that may provide this specific guidance include manufacturer's manuals, training programs, and reference guides.
   2. FIS should not serve as the sole source of aviation weather and other operational information. ATC, FSSs, and, if applicable, AOCC VHF/HF voice remain as a redundant method of communicating aviation weather, NOTAMs, and other operational information to aircraft in flight. FIS augments these traditional ATC/FSS/AOCC services and, for some products, offers the advantage of being displayed as graphical information. By using FIS for orientation, the usefulness of information received from conventional means may be enhanced. For example, FIS may alert the pilot to specific areas of concern that will more accurately focus requests made to FSS or AOCC for inflight updates or similar queries made to ATC.
   3. The airspace and aeronautical environment is constantly changing. These changes occur quickly and without warning. Critical operational decisions should be based on use of the most current and appropriate data available. When differences exist between FIS and information obtained by voice communication with ATC, FSS, and/or AOCC (if applicable), pilots are cautioned to use the most recent data from the most authoritative source.
   4. FIS aviation weather products (for example, graphical ground-based radar precipitation depictions) are not appropriate for tactical (typical timeframe of less than 3 minutes) avoidance of severe weather such as negotiating a path through a weather hazard area. FIS supports strategic (typical timeframe of 20 minutes or more) weather decision-making such as route selection to avoid a weather hazard area in its entirety. The misuse of information beyond its applicability may place the pilot and aircraft in jeopardy. In addition, FIS should never be used in lieu of an individual preflight weather and flight planning briefing.
   5. DSPs offer numerous MET and AI products with information that can be layered on top of each other. Pilots need to be aware that too much information can have a negative effect on their cognitive work load. Pilots need to manage the amount of information to a level that offers the most pertinent information to that specific flight without creating a cockpit distraction. Pilots may need to adjust the amount of information based on numerous factors including, but not limited to, the phase of flight, single pilot operation, autopilot availability, class of airspace, and the weather conditions encountered.
   6. FIS NOTAM products, including Temporary Flight Restriction (TFR) information, are advisory-use information and are intended for situational awareness purposes only. Cockpit displays of this information are not appropriate for tactical navigation - pilots should stay clear of any geographic area displayed as a TFR NOTAM. Pilots should contact FSSs and/or ATC while en route to obtain updated information and to verify the cockpit display of NOTAM information.
   7. FIS supports better pilot decision-making by increasing situational awareness. Better decision-making is based on using information from a variety of sources. In addition to FIS, pilots should take advantage of other weather/NAS status sources, including, briefings from Flight Service Stations, data from other air traffic control facilities, airline operation control centers, pilot reports, as well as their own observations.
5. FAA's Flight Information Service-Broadcast (FIS-B).
   1. FIS-B is a ground-based broadcast service provided through the FAA's Automatic Dependent Surveillance–Broadcast (ADS-B) Services Universal Access Transceiver (UAT) network. The service provides users with a 978 MHz data link capability when operating within range and line-of-sight of a transmitting ground station. FIS-B enables users of properly-equipped aircraft to receive and display a suite of broadcast weather and aeronautical information products.
   2. TBL 7-1-3 lists the text and graphical products available through FIS-B and provided free-of-charge. Detailed information concerning FIS-B meteorological products can be found in FAA-H-8083-28, Aviation Weather Handbook, and AC 00–63, Use of Cockpit Displays of Digital Weather and Aeronautical Information. Information on Special Use Airspace (SUA), Temporary Flight Restriction (TFR), and Notice to Airmen (NOTAM) products can be found in Chapters 3, 4, and 5 of this manual.
   3. Users of FIS-B should familiarize themselves with the operational characteristics and limitations of the system, including: system architecture; service environment; product lifecycles; modes of operation; and indications of system failure.
   4. FIS-B products are updated and transmitted at specific intervals based primarily on product issuance criteria. Update intervals are defined as the rate at which the product data is available from the source for transmission. Transmission intervals are defined as the amount of time within which a new or updated product transmission must be completed and/or the rate or repetition interval at which the product is rebroadcast. Update and transmission intervals for each product are provided in TBL 7-1-3.
   5. Where applicable, FIS-B products include a look-ahead range expressed in nautical miles (NM) for three service domains: Airport Surface; Terminal Airspace; and En Route/Gulf of America. TBL 7-1-4 provides service domain availability and look-ahead ranging for each FIS-B product.
   6. Prior to using this capability, users should familiarize themselves with the operation of FIS-B avionics by referencing the applicable User's Guides. Guidance concerning the interpretation of information displayed should be obtained from the appropriate avionics manufacturer.
   7. FIS-B malfunctions not attributed to aircraft system failures or covered by active NOTAM should be reported by radio or telephone to the nearest FSS facility, or by sending an email to the ADS-B help desk at adsb@faa.gov. Reports should include:
      1. Condition observed;
      2. Date and time of observation;
      3. Altitude and location of observation;
      4. Type and call sign of the aircraft; and
      5. Type and software version of avionics system.
6. Non-FAA FIS Systems. Several commercial vendors also provide customers with FIS data over both the aeronautical spectrum and on other frequencies using a variety of data link protocols. In some cases, the vendors provide only the communications system that carries customer messages, such as the Aircraft Communications Addressing and Reporting System (ACARS) used by many air carrier and other operators.
   1. Operators using non-FAA FIS data for inflight weather and other operational information should ensure that the products used conform to FAA/NWS standards. Specifically, aviation weather and NAS status information should meet the following criteria:
      1. The products should be either FAA/NWS “accepted” aviation weather reports or products, or based on FAA/NWS accepted aviation weather reports or products. If products are used which do not meet this criteria, they should be so identified. The operator must determine the applicability of such products to their particular flight operations.
      2. In the case of a weather product which is the result of the application of a process which alters the form, function or content of the base FAA/NWS accepted weather product(s), that process, and any limitations to the application of the resultant product, should be described in the vendor's user guidance material. An example would be a NEXRAD radar composite/mosaic map, which has been modified by changing the scaling resolution. The methodology of assigning reflectivity values to the resultant image components should be described in the vendor's guidance material to ensure that the user can accurately interpret the displayed data.

         TBL 7-1-3
         FIS-B Over UAT Product Update and Transmission Intervals

         Product	Update Interval1	Transmission Interval (95%)2	Basic Product
         AIRMET	As Available	5 minutes	Yes
         AWW/WW	As Available, then at 15 minute intervals for 1 hour	5 minutes	No
         Ceiling	As Available	10 minutes	No
         Convective SIGMET	As Available, then at 15 minute intervals for 1 hour	5 minutes	Yes
         D-ATIS	As Available	1 minute	No
         Echo Top	5 minutes	5 minutes	No
         METAR/SPECI	1 minute (where available), As Available otherwise	5 minutes	Yes
         MRMS NEXRAD (CONUS)	2 minutes	15 minutes	Yes
         MRMS NEXRAD (Regional)	2 minutes	2.5 minutes	Yes
         NOTAMs-D/FDC	As Available	10 minutes	Yes
         NOTAMs-TFR	As Available	10 minutes	Yes
         PIREP	As Available	10 minutes	Yes
         SIGMET	As Available, then at 15 minute intervals for 1 hour	5 minutes	Yes
         SUA Status	As Available	10 minutes	Yes
         TAF/AMEND	6 Hours (±15 minutes)	10 minutes	Yes
         Temperature Aloft	12 Hours (±15 minutes)	10 minutes	Yes
         TWIP	As Available	1 minute	No
         Winds aloft	12 Hours (±15 minutes)	10 minutes	Yes
         Lightning strikes 3	5 minutes	5 minutes	Yes
         Turbulence 3	1 minute	15 minutes	Yes
         Icing, Forecast Potential (FIP) 3	60 minutes	15 minutes	Yes
         Cloud tops 3	30 minutes	15 minutes	Yes
         1 Minute AWOS 3	1 minute	10 minutes	No
         Graphical-AIRMET 3	As Available	5 minutes	Yes
         Center Weather Advisory (CWA) 3	As Available	10 minutes	Yes
         Temporary Restricted Areas (TRA)	As Available	10 minutes	Yes
         Temporary Military Operations Areas (TMOA)	As Available	10 minutes	Yes

         ¹The Update Interval is the rate at which the product data is available from the source.

         ² The Transmission Interval is the amount of time within which a new or updated product transmission must be completed (95%) and the rate or repetition interval at which the product is rebroadcast (95%).

         ³ The transmission and update intervals for the expanded set of basic meteorological products may be adjusted based on FAA and vendor agreement on the final product formats and performance requirements.

         TBL 7-1-4
         Product Parameters for Low/Medium/High Altitude Tier Radios

         Product	Surface Radios	Low Altitude Tier	Medium Altitude Tier	High Altitude Tier
         CONUS NEXRAD	N/A	CONUS NEXRAD not provided	CONUS NEXRAD imagery	CONUS NEXRAD imagery
         Winds & Temps Aloft	500 NM look-ahead range	500 NM look-ahead range	750 NM look-ahead range	1,000 NM look-ahead range
         METAR	100 NM look-ahead range	250 NM look-ahead range	375 NM look-ahead range	CONUS: CONUS Class B & C airport METARs and 500 NM look-ahead range Outside of CONUS: 500 NM look-ahead range
         TAF	100 NM look-ahead range	250 NM look-ahead range	375 NM look-ahead range	CONUS: CONUS Class B & C airport TAFs and 500 NM look-ahead range Outside of CONUS: 500 NM look-ahead range
         AIRMET, SIGMET, PIREP, and SUA/SAA	100 NM look-ahead range. PIREP/SUA/SAA is N/A.	250 NM look-ahead range	375 NM look-ahead range	500 NM look-ahead range
         Regional NEXRAD	150 NM look-ahead range	150 NM look-ahead range	200 NM look-ahead range	250 NM look-ahead range
         NOTAMs D, FDC, and TFR	100 NM look-ahead range	100 NM look-ahead range	100 NM look-ahead range	100 NM look-ahead range

7-1-10. Weather Observing Programs

1. Manual Observations. With only a few exceptions, these reports are from airport locations staffed by FAA personnel who manually observe, perform calculations, and enter these observations into the (WMSCR) communication system. The format and coding of these observations are contained in paragraph 7-1-28 , Key to Aviation Routine Weather Report (METAR) and Aerodrome Forecasts (TAF).
2. Automated Weather Observing System (AWOS).
   1. Automated weather reporting systems are increasingly being installed at airports. These systems consist of various sensors, a processor, a computer‐generated voice subsystem, and a transmitter to broadcast local, minute‐by‐minute weather data directly to the pilot.
   2. The AWOS observations will include the prefix “AUTO” to indicate that the data are derived from an automated system. Some AWOS locations will be augmented by certified observers who will provide weather and obstruction to vision information in the remarks of the report when the reported visibility is less than 7 miles. These sites, along with the hours of augmentation, are to be published in the Chart Supplement. Augmentation is identified in the observation as “OBSERVER WEATHER.” The AWOS wind speed, direction and gusts, temperature, dew point, and altimeter setting are exactly the same as for manual observations. The AWOS will also report density altitude when it exceeds the field elevation by more than 1,000 feet. The reported visibility is derived from a sensor near the touchdown of the primary instrument runway. The visibility sensor output is converted to a visibility value using a 10-minute harmonic average. The reported sky condition/ceiling is derived from the ceilometer located next to the visibility sensor. The AWOS algorithm integrates the last 30 minutes of ceilometer data to derive cloud layers and heights. This output may also differ from the observer sky condition in that the AWOS is totally dependent upon the cloud advection over the sensor site.
   3. These real‐time systems are operationally classified into nine basic levels:
      1. AWOS-Aonly reports altimeter setting;
      2. AWOS-AV reports altimeter and visibility;
      3. AWOS-l usually reports altimeter setting, wind data, temperature, dew point, and density altitude;
      4. AWOS-2 provides the information provided by AWOS-l plus visibility; and
      5. AWOS-3 provides the information provided by AWOS-2 plus cloud/ceiling data.
      6. AWOS- 3P provides reports the same as the AWOS 3 system, plus a precipitation identification sensor.
      7. AWOS- 3PT reports the same as the AWOS 3P System, plus thunderstorm/lightning reporting capability.
      8. AWOS- 3T reports the same as AWOS 3 system and includes a thunderstorm/lightning reporting capability.
      9. AWOS- 4 reports the same as the AWOS 3 system, plus precipitation occurrence, type and accumulation, freezing rain, thunderstorm, and runway surface sensors.
   4. The information is transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID. AWOS transmissions on a discrete VHF radio frequency are engineered to be receivable to a maximum of 25 NM from the AWOS site and a maximum altitude of 10,000 feet AGL. At many locations, AWOS signals may be received on the surface of the airport, but local conditions may limit the maximum AWOS reception distance and/or altitude. The system transmits a 20 to 30 second weather message updated each minute. Pilots should monitor the designated frequency for the automated weather broadcast. A description of the broadcast is contained in subparagraph c. There is no two‐way communication capability. Most AWOS sites also have a dial‐up capability so that the minute‐by‐minute weather messages can be accessed via telephone.
   5. AWOS information (system level, frequency, phone number, etc.) concerning specific locations is published, as the systems become operational, in the Chart Supplement, and where applicable, on published Instrument Approach Procedures. Selected individual systems may be incorporated into nationwide data collection and dissemination networks in the future.
3. AWOS Broadcasts. Computer‐generated voice is used in AWOS to automate the broadcast of the minute‐by‐minute weather observations. In addition, some systems are configured to permit the addition of an operator‐generated voice message; e.g., weather remarks following the automated parameters. The phraseology used generally follows that used for other weather broadcasts. Following are explanations and examples of the exceptions.
   1. Location and Time. The location/name and the phrase “AUTOMATED WEATHER OBSERVATION,” followed by the time are announced.
      1. If the airport's specific location is included in the airport's name, the airport's name is announced.
      2. If the airport's specific location is not included in the airport's name, the location is announced followed by the airport's name.
      3. The word “TEST” is added following “OBSERVATION” when the system is not in commissioned status.
      4. The phrase “TEMPORARILY INOPERATIVE” is added when the system is inoperative.
   2. Visibility.
      1. The lowest reportable visibility value in AWOS is “less than ¹/₄.” It is announced as “VISIBILITY LESS THAN ONE QUARTER.”
      2. A sensor for determining visibility is not included in some AWOS. In these systems, visibility is not announced. “VISIBILITY MISSING” is announced only if the system is configured with a visibility sensor and visibility information is not available.
   3. Weather. In the future, some AWOSs are to be configured to determine the occurrence of precipitation. However, the type and intensity may not always be determined. In these systems, the word “PRECIPITATION” will be announced if precipitation is occurring, but the type and intensity are not determined.
   4. Ceiling and Sky Cover.
      1. Ceiling is announced as either “CEILING” or “INDEFINITE CEILING.” With the exception of indefinite ceilings, all automated ceiling heights are measured.
      2. The word “Clear” is not used in AWOS due to limitations in the height ranges of the sensors. No clouds detected is announced as “NO CLOUDS BELOW XXX” or, in newer systems as “CLEAR BELOW XXX” (where XXX is the range limit of the sensor).
      3. A sensor for determining ceiling and sky cover is not included in some AWOS. In these systems, ceiling and sky cover are not announced. “SKY CONDITION MISSING” is announced only if the system is configured with a ceilometer and the ceiling and sky cover information is not available.
   5. Remarks. If remarks are included in the observation, the word “REMARKS” is announced following the altimeter setting.
      1. Automated “Remarks.”
         1. Density Altitude.
         2. Variable Visibility.
         3. Variable Wind Direction.
      2. Manual Input Remarks. Manual input remarks are prefaced with the phrase “OBSERVER WEATHER.” As a general rule the manual remarks are limited to:
         1. Type and intensity of precipitation.
         2. Thunderstorms and direction; and
         3. Obstructions to vision when the visibility is 3 miles or less.
      3. If an automated parameter is “missing” and no manual input for that parameter is available, the parameter is announced as “MISSING.” For example, a report with the dew point “missing” and no manual input available, would be announced as follows:
      4. “REMARKS” are announced in the following order of priority:
         1. Automated “REMARKS.”
            1. Density Altitude.
            2. Variable Visibility.
            3. Variable Wind Direction.
         2. Manual Input “REMARKS.”
            1. Sky Condition.
            2. Visibility.
            3. Weather and Obstructions to Vision.
            4. Temperature.
            5. Dew Point.
            6. Wind; and
            7. Altimeter Setting.
4. Automated Surface Observing System (ASOS)/Automated Weather Observing System (AWOS) The ASOS/AWOS is the primary surface weather observing system of the U.S. (See Key to Decode an ASOS/AWOS (METAR) Observation, FIG 7-1-8 and FIG 7-1-9.) The program to install and operate these systems throughout the U.S. is a joint effort of the NWS, the FAA and the Department of Defense. ASOS/AWOS is designed to support aviation operations and weather forecast activities. The ASOS/AWOS will provide continuous minute‐by‐minute observations and perform the basic observing functions necessary to generate an aviation routine weather report (METAR) and other aviation weather information. The information may be transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID. ASOS/AWOS transmissions on a discrete VHF radio frequency are engineered to be receivable to a maximum of 25 NM from the ASOS/AWOS site and a maximum altitude of 10,000 feet AGL. At many locations, ASOS/AWOS signals may be received on the surface of the airport, but local conditions may limit the maximum reception distance and/or altitude. While the automated system and the human may differ in their methods of data collection and interpretation, both produce an observation quite similar in form and content. For the “objective” elements such as pressure, ambient temperature, dew point temperature, wind, and precipitation accumulation, both the automated system and the observer use a fixed location and time‐averaging technique. The quantitative differences between the observer and the automated observation of these elements are negligible. For the “subjective” elements, however, observers use a fixed time, spatial averaging technique to describe the visual elements (sky condition, visibility and present weather), while the automated systems use a fixed location, time averaging technique. Although this is a fundamental change, the manual and automated techniques yield remarkably similar results within the limits of their respective capabilities.
   1. System Description.
      1. The ASOS/AWOS at each airport location consists of these main components:
         1. Individual weather sensors.
         2. Data collection and processing units.
         3. Peripherals and displays.
      2. The ASOS/AWOS sensors perform the basic function of data acquisition. They continuously sample and measure the ambient environment, derive raw sensor data and make them available to the collection and processing units.
   2. Every ASOS/AWOS will contain the following basic set of sensors:
      1. Cloud height indicator (one or possibly three).
      2. Visibility sensor (one or possibly three).
      3. Precipitation identification sensor.
      4. Freezing rain sensor (at select sites).
      5. Pressure sensors (two sensors at small airports; three sensors at large airports).
      6. Ambient temperature/Dew point temperature sensor.
      7. Anemometer (wind direction and speed sensor).
      8. Rainfall accumulation sensor.
      9. Automated Lightning Detection and Reporting System (ALDARS) (excluding Alaska and Pacific Island sites).
   3. The ASOS/AWOS data outlets include:
      1. Those necessary for on‐site airport users.
      2. National communications networks.
      3. Computer‐generated voice (available through FAA radio broadcast to pilots, and dial‐in telephone line).
   4. An ASOS/AWOS report without human intervention will contain only that weather data capable of being reported automatically. The modifier for this METAR report is “AUTO.” When an observer augments or backs-up an ASOS/AWOS site, the “AUTO” modifier disappears.
   5. There are two types of automated stations, AO1 for automated weather reporting stations without a precipitation discriminator, and AO2 for automated stations with a precipitation discriminator. As appropriate, “AO1” and “AO2” must appear in remarks. (A precipitation discriminator can determine the difference between liquid and frozen/freezing precipitation).

      FIG 7-1-8
      Key to Decode an ASOS/AWOS (METAR) Observation (Front)

      

      FIG 7-1-9
      Key to Decode an ASOS/AWOS (METAR) Observation (Back)

      

5. TBL 7-1-5contains a comparison of weather observing programs and the elements reported.
6. Service Standards. During 1995, a government/industry team worked to comprehensively reassess the requirements for surface observations at the nation's airports. That work resulted in agreement on a set of service standards, and the FAA and NWS ASOS sites to which the standards would apply. The term “Service Standards” refers to the level of detail in weather observation. The service standards consist of four different levels of service (A, B, C, and D) as describedbelow. Specific observational elements included in each service level are listed in TBL 7-1-6.
   1. Service Level D defines the minimum acceptable level of service. It is a completely automated service in which the ASOS/AWOS observation will constitute the entire observation, i.e., no additional weather information is added by a human observer. This service is referred to as a stand alone D site.
   2. Service Level C is a service in which the human observer, usually an air traffic controller, augments or adds information to the automated observation. Service Level C also includes backup of ASOS/AWOS elements in the event of an ASOS/AWOS malfunction or an unrepresentative ASOS/AWOS report. In backup, the human observer inserts the correct or missing value for the automated ASOS/AWOS elements. This service is provided by air traffic controllers under the Limited Aviation Weather Reporting Station (LAWRS) process, FSS and NWS observers, and, at selected sites, Non-Federal Observation Program observers.

      Two categories of airports require detail beyond Service Level C in order to enhance air traffic control efficiency and increase system capacity. Services at these airports are typically provided by contract weather observers, NWS observers, and, at some locations, FSS observers.

   3. Service Level B is a service in which weather observations consist of all elements provided under Service Level C, plus augmentation of additional data beyond the capability of the ASOS/AWOS. This category of airports includes smaller hubs or special airports in other ways that have worse than average bad weather operations for thunderstorms and/or freezing/frozen precipitation, and/or that are remote airports.
   4. Service Level A, the highest and most demanding category, includes all the data reported in Service Standard B, plus additional requirements as specified. Service Level A covers major aviation hubs and/or high volume traffic airports with average or worse weather.

      TBL 7-1-5
      Weather Observing Programs

      Type

      ASOS

      X

      X

      X

      X

      X

      X

      X

      X

      X

      X

      AWOS-A

      X

      AWOS-A/V

      X

      X

      AWOS-1

      X

      X

      X

      X

      AWOS-2

      X

      X

      X

      X

      X

      AWOS-3

      X

      X

      X

      X

      X

      X

      AWOS-3P

      X

      X

      X

      X

      X

      X

      X

      AWOS-3T

      X

      X

      X

      X

      X

      X

      X

      AWOS-3P/T

      X

      X

      X

      X

      X

      X

      X

      X

      AWOS-4

      X

      X

      X

      X

      X

      X

      X

      X

      X

      X

      X

      X

      Manual

      X

      X

      X

      X

      X

      X

      X

      REFERENCE- FAA Order JO 7900.5, Surface Weather Observing, for element reporting.

      TBL 7-1-6
      

      				SERVICE LEVEL A
      				Service Level A consists of all the elements of Service Levels B, C and D plus the elements listed to the right, if observed.	10 minute longline RVR at precedented sites or additional visibility increments of 1/8, 1/16 and 0 Sector visibility Variable sky condition Cloud layers above 12,000 feet and cloud types Widespread dust, sand and other obscurations Volcanic eruptions
      			SERVICE LEVEL B
      			Service Level B consists of all the elements of Service Levels C and D plus the elements listed to the right, if observed.		Longline RVR at precedented sites (may be instantaneous readout) Freezing drizzle versus freezing rain Ice pellets Snow depth & snow increasing rapidly remarks Thunderstorm and lightning location remarks Observed significant weather not at the station remarks
      		SERVICE LEVEL C
      		Service Level C consists of all the elements of Service Level D plus augmentation and backup by a human observer or an air traffic control specialist on location nearby. Backup consists of inserting the correct value if the system malfunctions or is unrepresentative. Augmentation consists of adding the elements listed to the right, if observed. During hours that the observing facility is closed, the site reverts to Service Level D.			Thunderstorms Tornadoes Hail Virga Volcanic ash Tower visibility Operationally significant remarks as deemed appropriate by the observer
      	SERVICE LEVEL D
      	This level of service consists of an ASOS or AWOS continually measuring the atmosphere at a point near the runway. The ASOS or AWOS senses and measures the weather parameters listed to the right.				Wind Visibility Precipitation/Obstruction to vision Cloud height Sky cover Temperature Dew point Altimeter